The Fed needs to drive down borrowing rates because the economy isn't growing fast enough to reduce high unemployment, Bernanke said in a speech to the Economic Club of Indiana. The unemployment rate is 8.1 percent.

Low rates could also help shrink the federal budget deficit by easing the government's borrowing costs and generating tax revenue from stronger growth, Bernanke argued.

The chairman cautioned Congress against adopting a law that would allow it to review the Fed's interest-rate policy discussions. The House has passed legislation to give Congress' investigative arm broader authority to audit the Fed, including reviewing its interest-rate policymaking. The Senate hasn't adopted the bill.

Bernanke warned that such a step would improperly inject political pressure into the Fed's private deliberations and make officials less likely to act.

His speech follows the Fed's decision at its Sept. 12-13 meeting to launch a new mortgage-buying program to try to help boost the housing market, spur hiring and accelerate economic growth. The Fed said it would keep buying the bonds until the job market showed substantial improvement. It also decided to keep its benchmark short-term interest rate near zero through at least mid-2015.

In his speech, Bernanke sought to reassure investors that the Fed's timetable for keeping rates low "doesn't mean we expect the economy to be weak through 2015." Rather, he said the Fed expects to keep rates low well after the economy strengthens.

Bernanke spoke two days before President Barack Obama and Republican challenger Mitt Romney will hold a debate in which the economy is the central theme. And on Friday, the government will release its September jobs report. Economists expect only modest hiring gains and continued unemployment above 8 percent.